S0 TrussThe
Starboard 0 (S-Zero) Truss segment is the first major element
of the International Space Station's enormous exterior framework.
The S0 Truss is 13.4 meters (44 feet) long and 4.6 meters (15
feet) wide and weighs 12,247 kilograms (27,000 pounds). It
is the center segment of nine integrated trusses that will provide
the foundation for station subsystem hardware installation, utility
distribution, power generation, heat rejection and external payload
accommodations. The S0 Truss acts as the junction from which external
utilities are routed to the pressurized modules by means of EVA-deployed
umbilicals.

The S0 is
going to the space station with a complement of pre-integrated
hardware to increase ISS functionality, including the Mobile Transporter,
the Trailing Umbilical System, the Portable Work Platform, four
Global Positioning System antennas, two rate gyros, an Extravehicular
Charged Particle Detection System and umbilicals for U.S. on-orbit
elements. Mission 8A also delivers four Main Bus Switching Units,
two Circuit Interrupt Devices, three Crew and Equipment Translation
Aid lights and the Airlock Spur.

Mobile
TransporterThe
Mobile Transporter (MT) will become the first railroad in space
on the International Space Station during STS-110.

The 885-kilogram
(1,950-pound) structure will travel along the rails of the Integrated
Truss Structure and, together with the Mobile Base System, will
provide the work platform for the station's robotic arm. The transporter
measures 274 centimeters (108 inches) long, 261 centimeters (103
inches) wide and 97 centimeters (38 inches) high.

During STS-110,
the MT will undergo a series of diagnostic tests on the S0 Truss
after power and data cables are connected and launch restraints
are removed. The Mobile Base System will be installed during STS-111
onto the MT to complete the Mobile Servicing System, eventually
giving Canadarm2 the capacity to move from the U.S. Destiny Laboratory
Module and travel the length of the Integrated Truss Structure.

What
is a payload?

The
formal designation as a "payload" indicates that the experiment
will be accorded top priority in crew time and energies during the
entire flight, along with all other experiments carrying the same
"payload" designation.